Pace Calculator (Running)

A pace calculator converts between pace (minutes per mile or km), speed and finish time for a given distance. If you know two of these three values, the calculator works out the third. Common UK race distances include parkrun (5 km), 10 km, half marathon (21.1 km) and marathon (42.2 km).

The calculator also generates split times for each kilometre or mile, which is useful for even pacing during a race. It can predict finish times for other distances using the Riegel formula, which estimates that pace slows by a known factor as distance increases.

Enter a distance and either your target time or pace. The calculator shows pace per km and per mile, average speed in km/h and mph, split tables and predicted finish times for standard distances. This helps with race planning and setting realistic targets based on training performance.

Running pace conversions. Pace = time per unit distance. Min/km to min/mile: multiply by 1.609. Sample paces — 5:00/km = 8:03/mile (sub-3 marathon pace 4:15/km = 6:50/mile). UK Parkrun (5km) average finishing time: 28:30 = 5:42/km = 9:11/mile. London Marathon average: 4:30 = 6:24/km = 10:18/mile. Elite marathon: 2:01 (men's WR Kelvin Kiptum) = 2:52/km = 4:37/mile.

How to predict race times from training paces. Riegel formula: T₂ = T₁ × (D₂/D₁)^1.06. Example: ran 10K in 50 min; predicted half-marathon: 50 × (21.1/10)^1.06 = 110 min (1:50). Predicted marathon: 50 × (42.2/10)^1.06 = 230 min (3:50). Caveat: assumes equal training for the distance. Most amateurs are 5-15% slower in marathons than Riegel predicts due to undertraining for the distance. Yasso 800s: marathon predictor — run 10 × 800m at average X minutes; marathon time = X hours and X minutes (e.g. 3:30 800s = 3:30 marathon).

Heart rate zones and pace correlation. Zone 1 (recovery): 50-60% max HR — conversational, very easy. Zone 2 (aerobic base): 60-70% — sustainable for hours, talking in sentences. Zone 3 (tempo): 70-80% — talking in 2-3 word phrases. Zone 4 (threshold): 80-90% — single words only, sustained ~1 hour max. Zone 5 (max): 90-100% — anaerobic, minutes only. Marathon pace = top end of Zone 2/bottom Zone 3. 10K pace = mid Zone 4. 5K pace = top Zone 4/bottom Zone 5.

UK running distance standards. Parkrun 5km — free, every Saturday 9am UK. UK record 13:31 (Marc Scott). Half marathon: 21.0975 km / 13.1 miles. Marathon: 42.195 km / 26.2 miles. Ultramarathon: anything above marathon. UK trail/fell running: distances often metric, terrain matters more than pace. London Marathon entry: ballot 1-in-15 chance; Good For Age qualifying times (e.g. M40 sub-3:15); charity place £2,000+ fundraising. Speed run: Bob Graham Round 66 miles 42 peaks 27,000 ft 24 hours — UK ultra-test piece.

Building pace gradually — training principles. 80/20 rule: 80% of training easy pace (Zone 1-2), 20% hard (Zone 4-5). Most amateurs do too much medium-effort, missing both base-building and intensity benefits. Long runs progress 5-10% weekly — never jump more than 25% in one week. Recovery weeks every 3-4 weeks (cut volume 25-30%). Easy pace should be 60-90 seconds/km slower than goal race pace. Tempo runs at threshold (max comfortable pace, sustainable 1 hour). Speed work: 400m, 800m, 1km repeats at faster than goal race pace.